<?xml version = '1.0' encoding = 'utf-8'?>
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <script>
      function doTest() {
        var Ci = Components.interfaces;
        var defaultZoom = {}, allowZoom = {}, minZoom = {}, maxZoom ={}, width = {}, height = {}, autoSize = {};
        var windowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
        windowUtils.getViewportInfo(1, 1, defaultZoom, allowZoom, minZoom, maxZoom, width, height, autoSize);
        document.getElementById("minZoom").innerHTML = minZoom.value.toPrecision(10);
        document.getElementById("maxZoom").innerHTML = maxZoom.value.toPrecision(10);
      }
    </script>
  </head>
  <body onload="doTest();">
  MinZoom: <span id="minZoom"></span><br />
  MaxZoom: <span id="maxZoom"></span>
  </body>
</html>
